1. Field of the Invention
The present invention relates generally to a method for serving of a station groups in the Internet protocol telephony exchange system, having a configuration to be able to control both IP terminals and legacy terminals by transceiving user information with IP terminals.
2. Description of the Related Art
Recently, as Internet is expanding rapidly to the vast majority of the world, and to meet the needs for a variety of different services, IP has been developed at a remarkable speed in terms of performances and services it provides to users. Not being satisfied here, users are continually asking for more diverse services. One of the examples is transmission of voice signals using IP network (or VoIP: Voice over Internet Protocol). Besides the data transmission of voice signals through such IP network, other manifold services associated with the voice signal transmission, yet they being a major part of the IP network, have been requested more and more.
As an attempt to meet the request, a technique for integrating generally used legacy telecommunication and VoIP is under development for interworking with a current communication network. For instance, integration of IP-based private automatic branch exchanges, i.e., IP-PBX (Internet Protocol PBX) and IP-Centrex, is the typical one. Therefore, to satisfy different needs of users, the terminals for use of IP network should be able to have the same format and same performances with those used for PSTN (Public Switching Telephone Network).
A general IP-phone protocol currently being used right now is one of H.323 recommended by ITU-T, MGCP (Media Gateway Control Protocol) used between a media gateway and a media gateway controller for controlling the media gateway, or SIP (Session Initiation Protocol), a multimedia communication standard supporting integration of data, voice and image.
Normally, IP network and PSTN are separated from each other, and therefore, terminals that are accessible to each net have different protocols and different characteristics. More specifically, terminals that are connectable to PSTN are subscriber terminals including analog telephones, digital telephones or modems, while terminals that are connectable to trunk connection part include E1/T1, PRI (primary rate interface), loop and No. 7 signaling and so forth. Further, terminals that are connectable to IP network include H.323 terminals, MGCP terminals, SIP terminals and so on. To transmit/receive voices using an IP-terminal and IP network, the terminal should be connected to IP-line through LAN and gatekeeper.
In other words, to enable IP network subscribers and PSTN subscribers to communicate with each other by interworking of IP network and PSTN, any type of gateway is necessary, and to seize such gateway, an independent system for seizing internetwork should be configured. This means that IP network and PSTN have their own mutually independent number systems and terminal management systems.
In case a general legacy terminal accommodated to PSTN calls another general legacy terminal, depending on the address of a called party's terminal (domestic, long-distance, overseas, wire/wireless), a pre-designated prefix is dialed to make the call. However, if the called party uses an IP terminal, it was essential to dial a prefix seizing a gateway that is connected to a corresponding exchange.
Similarly, users having IP terminal connected over Internet should dial a pre-designated prefix in conforming to the address of the other party (domestic or other areas). And, if it is necessary to make a call to PSTN, users must dial a prefix for seizing a gateway that is connected to an exchange system to control the other party's terminal.
However, according to the conventional technology described above, mutually independent systems are in charge of controlling calls between PSTN based terminals and IP network based terminals. Thus, to configure voice channels between IP terminals and legacy terminals, two separate systems are required. This means that a service should be carried out independently over the interwork of the two systems, and integrated function and terminal management system over internetwork is therefore impossible. Unfortunately, this made it very difficult to integrate IP terminals in areas using the existing PSTN or within a building. That is, implementation of an IP based internal private automatic branch exchange got very complicated since PBX cannot process calls from IP terminals like extension telephones, and as a result thereof, a number of services provided by PBX were not available.
For example, station group services and ring group services from the local private automatic branch exchange cannot be provided. The station group service indicates a service where a plurality of terminals are registered to the exchange as one station group, each station group having a general directory number, so when a caller makes a phone call to the general directory number of the station group, the call reaches a subscriber to whom the call can be received in conforming to the group service system. Such station group service uses a system like “HUNT, DISTRIBUTION, EQUALITY” and so forth.
Similarly, the ring group service (or group call pickup) indicates a service where a plurality of terminals are registered to the exchange as one ring group, each station group having a general directory number, so when a caller makes a phone call to the general directory number of the ring group, the call reaches any member of the ring group who is in an idle state at the moment. And, if one member answers the phone, other members do not hear the ring any more. At this time, if every member of the ring group happens to be in middle of conversation over the phone, the call is queued for a second. Then, as soon as there is a member who finished his or her call, the call in queue mode is connected right to the member available.
However, in the conventional IP-PBX a legacy terminal connected to PBX and an IP terminal connected to an IP network had different systems from each other. This consequently made the IP-PBX unable to provide station group services that are typically available in the PBX because it could connect only traffic channels through a gateway.